A High-Energy-Density Aqueous Zinc-Manganese Battery with a La-Ca Co-Doped ε-MnO2 Cathode
Aqueous zinc-manganese dioxide batteries (Zn//MnO2) are gaining considerable research attention for energy storage taking advantages of their low cost and high safety. However, the capacity and cycling stability of the state-of-the-art devices are still utterly disappointing because of the inevitable MnO2 dissolution and its low conductivity. In this work, to elevate the energy density of Zn//MnO2, a La-Ca co-doping strategy is proposed to boost the electrochemical performance of the ε-MnO2 cathode. Specifically, the introduction of heteroatoms, La3+ and Ca2+, is achieved via a facile one-step liquid coprecipitation method. Our experimental results reveal that Ca2+ significantly improves the stability of ε-MnO2 while Ca2+ and La3+ both contribute to the capacity and reversibility enhancement. Therefore, the overall performance of the La-Ca co-doped ε-MnO2 cathode exceeds the pristine sample, as demonstrated by its commendable capacity of 297.3 mAh g-1 at 0.2 A g-1, superior cycle stability (up to 76.8% capacity retention after 200 cycles) and excellent rate ability (161 mAh g-1 when the current density increased to 1.6 A g-1). Besides, the assembled Zn//ε-MnO2 device delivers a maximum energy and power density of 401.22 Wh kg-1 and 5.2 kW kg-1 respectively, outperforming most of recently reported Zn//MnO2 counterparts.